1. Field of the Invention
The present invention is directed generally to a filter and, more particularly, to filters including capacitively coupled resonators and filters including resonators integral with a housing. The present invention is also directed to methods of making a filter.
2. Description of the Background
Filters utilizing stepped impedance resonators (SIRs) have been realized in various media, such as printed microstrip circuits, stripline, dielectric block, and air dielectric. Microstrip and stripline filters, however, often require the use of expensive substrate material and labor intensive assembly. Moreover, the electrical performance of such filters diminishes at lower frequencies, such as below about 400 MHz. Dielectric block resonators typically require the use of expensive dielectric material, which are additionally too heavy for certain applications. Furthermore, dielectric block resonators exhibit insertion loss, which is the loss of signal energy as the signal passes through the filter, which varies significantly based upon the type of dielectric used. Air dielectric combline filters use distributed capacitive coupling, which limits the bandwidth of the filter.
Accordingly, there exists a need for a filter that is small and light weight, and which maintains satisfactory electrical performance characteristics. Also, a need exists for such a filter which is operable at lower frequency ranges. In addition, there exists a need for a such a filter which allows for a wider range of bandwidths.